Evaluation of Very High Cycle Fatigue Properties of Low Temperature Nitrided Ti-6Al-4V Alloy Using Ultrasonic Testing Technology

Abstract:

Fatigue tests were carried out at the stress ratio R = -1 using a 20 kHz ultrasonic testing facility to investigate the effects of low temperature nitriding on the fatigue properties of Ti-6Al-4V alloy in the very high cycle fatigue (VHCF) regime in detail. The oscillation and fatigue behavior of the nitrided Ti-alloy were characterized by measuring parameters like the ultrasonic generator power, the displacement of the specimens and dissipated energy under ultrasonic cyclic load. Moreover, the surface microstructure of the nitrided Ti-alloy was characterized using a micro-Vickers hardness tester, an optical microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron backscatter diffraction technique (EBSD) to clarify the fatigue fracture mechanism. The Ti-alloy nitrided at the temperature of 873 K showed duplex S-N properties consisting of the respective fracture modes of the surface fracture and the subsurface fracture. The low temperature nitriding reduced the surface fatigue life of Ti-alloy in comparison to the un-nitrided one due to the formation of a brittle titanium nitride (T_i2N), whereas the subsurface fatigue life in the VHCF regime was increased by the low temperature nitriding. In addition, the fatigue fracture mechanisms of the low temperature nitrided Ti-alloy were discussed from viewpoints of fractography and fracture mechanics.

• Periodical: Key Engineering Materials (Volume 664)
• Pages: 118-127
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.664.118
• Online since: September 2015
• Authors: Shoichi Kikuchi*, Stefan Heinz, Dietmar Eifler, Yuta Nakamura, Akira Ueno
• Keywords: Fish-Eye, Fractography, Nitriding, Titanium Alloy, Very High Cycle Fatigue

References

[1] W. P. Tong, C. Z. Liu, W. Wang, N. R. Tao, Z. B. Wang, L. Zuo, J. C. He, Gaseous nitriding of iron with a nanostructured surface layer. Scripta Mater., 57 (2007) 533-536.

DOI: 10.1016/j.scriptamat.2007.05.017

[2] A. Alsaran, Determination of tribological properties of ion-nitrided AISI 5140 steel. Mater. Char., 49 (2002) 171-176.

DOI: 10.1016/s1044-5803(03)00008-1

[3] T. Morita, H. Takahashi, M. Shimizu, K. Kawasaki, Factors controlling the fatigue strength of nitride titanium. Fatig. Fract. Eng. Mater. Struct., 20 (1997) 85–92.

DOI: 10.1111/j.1460-2695.1997.tb00404.x

[4] H. Shibata, K. Tokaji, T. Ogawa, C. Hori, The effect of gas nitriding on fatigue behavior in titanium alloys, Int. J Fatig. 16 (1994) 370–376.

DOI: 10.1016/0142-1123(94)90448-0

[5] S. Kikuchi, Y. Nakamura, A. Ueno, K. Ameyama, Development of low temperature nitriding process and its effects on the 4-points bending fatigue properties of commercially pure titanium. Adv. Mater. Res., 891-892 (2014) 656–661.

DOI: 10.4028/www.scientific.net/amr.891-892.656

[6] A.J. McEvily, T. Nakamura, H. Oguma, K. Yamashita, H. Matsunaga and M. Endo, On the mechanism of very high cycle fatigue in Ti-6Al-4V. Scripta Mater., 59 (2008) 1207–1209.

DOI: 10.1016/j.scriptamat.2008.08.012

[7] H. Oguma and T. Nakamura, The effect of microstructure on very high cycle fatigue properties in Ti-6Al-4V. Scripta Mater., 63 (2010) 32–34.

DOI: 10.1016/j.scriptamat.2010.02.043

[8] S. Heinz, F. Balle, G. Wagner, D. Eifler, Analysis of fatigue properties and failure mechanisms of Ti6Al4V in the very high cycle fatigue regime using ultrasonic technology and 3D laser scanning vibrometry. Ultrasonics, 53 (2013) 1433–1440.

DOI: 10.1016/j.ultras.2013.03.002

[9] S. Heinz, F. Balle, G. Wagner, D. Eifler, Innovative ultrasonic testing facility for fatigue experiments in the VHCF regime. Mater. Test., 54 (2012) 750–755.

DOI: 10.3139/120.110395

[10] T. Sakai, Review and prospects for current studies on very high cycle fatigue of metallic materials for machine structural use. J Solid Mech. Mater. Eng., 3 (2009) 1573-1587.

DOI: 10.1299/jmmp.3.425

[11] K. S. R. Chandran, P. Chang, G. T. Cashman, Competing failure modes and complex S-N curves in fatigue of structural materials. Int. J Fatig., 32 (2010) 482-491.

DOI: 10.1016/j.ijfatigue.2009.08.004

[12] G. T. Cashman, A review of competing modes fatigue behavior. Int. J Fatig., 32 (2010) 492-496.

[13] K. Shiozawa, M. Murai, Y. Shimatani, T. Yoshimoto, Transition of fatigue failure mode of Ni-Cr-Mo low-alloy steel in very high cycle regime. Int. J Fatig., 32 (2010) 541-550.

DOI: 10.1016/j.ijfatigue.2009.06.011

[14] D. F. Neal, P. A. Blenkinsop, Internal fatigue origins in a-b titanium alloys. Acta Metall., 24 (1976) 59-63.

DOI: 10.1016/0001-6160(76)90147-4

[15] Y. Murakami, M. Endo, Effects of defects, inclusions and inhomogeneities on fatigue strength. Int. J Fatig., 16 (1994), 163-182.

DOI: 10.1016/0142-1123(94)90001-9